1. Field of the Invention
The present invention relates generally to magnetic heads that are utilized with thin film hard disk data storage devices, and more particularly to the design and fabrication of a magnetic head having an optical energy resonant cavity storage media heating device.
2. Description of the Prior Art
Hard disk drives generally include one or more rotatable data storage disks having a magnetic data storage layer formed thereon. Data in the form of small magnetized areas, termed magnetic data bits, are written onto the magnetic layers of the disks by a magnetic head that includes magnetic poles through which magnetic flux is caused to flow. Magnetic flux flowing from a pole tip portion of the magnetic poles in close proximity to the magnetic layer on the disk, causes the formation of the magnetic bits within the magnetic layer.
The continual quest for higher data recording densities of the magnetic media demands smaller magnetic data bit cells, in which the volume of recording material (grains) in the cells is decreased and/or the coercivity (Hc) is increased. When the bit cell size is sufficiently reduced, the problem of the superparamagnetic limit will provide a physical limit of the magnetic recording areal density. Present methods to delay the onset of this limit in storage media include the use of higher magnetic moment materials, and using thermally assisted recording (TAR) heads. The present invention relates to such thermally assisted recording heads in which a heating device is disposed within the magnetic head. Heat from the heating device temporarily reduces the localized coercivity of the magnetic media, such that the magnetic head is able to record data bits within the media. Once the disk returns to ambient temperature, the very high coercivity of the magnetic media provides the bit stability necessary for the recorded data disk.
In using optical energy for the heating of the magnetic medium, one needs to consider the applicability of the optics in near field, e.g., 1 to 20 nm from the source which resides in the magnetic head slider, and the heating of an area in the medium of very small dimensions, e.g., in the 20 to 30 nm range. Conventional diffraction limited optics is not applicable for such a small area. Recently, descriptions of several TAR methods for near-field heating of media have been published. In published U.S. patent applications US2003/0184903 A1 and US2004/0008591 A1 special ridged waveguides are used as high transmission apertures disposed within the magnetic head are taught for applications in perpendicular recording. In general the size of the heated spot depends on the optical wavelength and the dimensions and the composition of the materials for the waveguide/ridged waveguide. For instance, the transmittance of sub-wavelength circular apertures decreases as r4 where r is the radius of the waveguide aperture. Thus the transmittance efficiency of sub-wavelength apertures is very poor and high power lasers would be required to heat the medium.
The present invention utilizes an optical resonant cavity to amplify the light intensity and thus increase overall efficiency of transmitting light from the laser source to the medium. Such resonant cavities include spherical cavities, disk shaped cavities, ring shaped cavities, racetrack shaped cavities, micropillar cavities, photonic crystal cavities and Fabry-Perot cavities. Such cavities are known to those skilled in the art and are described in articles such as “Optical Microcavities” by Kerry J. Vahala, Nature, vol. 34, 14 Aug. 2003, page 839-846. The coupling of power into the optical resonant cavity may be by way of evanescent-wave coupling from an optical fiber or integrated waveguide. As a prior art example of this, R. W. Boyd et al., in Journal of Modern Optics, 2003, Vol. 50, No.15-17, 2543-2550, “Nanofabrication of optical structures and devices for photonics and biophotonics” teaches a system consisting of a waveguide coupled to a resonant whispering gallery mode (WGM) cavity. In this technique a tapered planar waveguide is placed within a gap that is a fraction of a wavelength from a resonant microcavity.
Much of the difficulty in applying near field optical devices for TAR lies in their incompatibility with the space-limited mechanical structure of the write poles within a magnetic head, the difficulty in bringing photons to such devices, and meeting the requirements for producing a near field high intensity optical beam that is within about 10 nm from the bit area that is being written. The heated spot is preferably at or a short distance uptrack of the write pole. Furthermore, many structures suggested for TAR heads are not readily compatible with current manufacturing processes, which rely on building planar structures perpendicular to the ABS with thin film deposition and etching techniques. The present invention facilitates the fabrication of the resonant cavity within the magnetic head structure at the wafer level of magnetic head fabrication.